Conductance asymmetry of graphene pn junction

TL;DR

This paper models the conductance of graphene pn junctions using NEGF, explaining experimental results and highlighting the importance of junction width and wavefunction mismatch in device performance.

Contribution

It provides a quantitative ballistic transport model for graphene pn junctions that accounts for junction width and wavefunction mismatch effects.

Findings

Finite junction transition width explains resistance asymmetry.

Wavefunction mismatch significantly affects conductance in sharp junctions.

Model aligns well with recent experimental observations.

Abstract

We use the non-equilibrium Green function (NEGF) method in the ballistic limit to provide a quantitative description of the conductance of graphene pn junctions - an important building block for graphene electronics devices. In this paper, recent experiments on graphene junctions are explained by a ballistic transport model, but only if the finite junction transition width, Dw, is accounted for. In particular, the experimentally observed anamolous increase in the resistance asymmetry between nn and np junctions under low source/drain charge density conditions is also quantitatively captured by our model. In light of the requirement for sharp junctions in applications such as electron focusing, we also examine the pn junction conductance in the regime where Dw is small and find that wavefunction mismatch (so-called pseudo-spin) plays a major role in sharp pn junctions.